In the first decades of the 20th century, when life was being transformed by scientific innovations, researchers made a thrilling new claim: they could tell whether someone was lying by using a machine. Popularly known as the “lie detector,” the device transformed police work, seized headlines and was extolled in movies, TV and comics as an infallible crime-fighting tool. Husbands and wives tested each other’s fidelity. Corporations routinely tested employees’ honesty and government workers were tested for loyalty and “morals.” But the promise of the polygraph turned dark, and the lie detector too often became an apparatus of fear and intimidation. The Lie Detector is a tale of good intentions, twisted morals and unintended consequences.